1. Field of the Invention
The present invention relates to a technology for a battery module including a plurality of cells, an electric storage device and an electric system.
2. Description of Related Art
Japanese Laid Open Patent Publication No. H10-3950 (patent literature 1) and Japanese Laid Open Patent Publication No. 2005-183343 (patent literature 2) disclose a technology for cooling cells.
Patent literature 1 discloses that a plurality of storage battery strings in which a plurality of cylindrical cells aligned with one another in the same axial direction are arranged in parallel. Patent literature 1 also discloses that a main cooling passage is formed between a dividing wall of a battery holding part and the storage battery strings and a sub cooling passage is formed between the battery holding parts in the horizontal direction, so as to supply a cooling medium along the storage battery strings and to allow the cooling medium to pass through the main cooling passage and the sub cooling passage. The technology disclosed in patent literature 1 allows the cooling medium passing through the sub cooling passage to merge into the cooling medium passing through the main cooling passage in the midstream or downstream, so as to reduce the temperature of the cooling medium which cools the cells arranged downward from the midstream or downstream in the storage battery strings, thereby improving the cooling efficiency of the cells arranged in the midstream or downstream in the storage battery strings.
Patent literature 2 discloses that a plurality of battery modules which include a plurality of cells serially connected and integrated into a rod shape are arranged in parallel and a staggered manner and cooling fluid is supplied from the direction along the plurality of battery modules. Patent literature 2 also discloses that a cooling air guide groove is formed in an inner surface of a battery case, whose cross-sectional area reduces along the direction from a cooling air inlet to a cooling air outlet. The technology disclosed in patent literature 2 allows the cooling air flowing through the cooling air guide groove to be guided from a vicinity of an intermediate point of a longitudinal side of the battery case to a middle battery module in a direction close to each other so as to cool the battery module effectively and reduce temperature rise in the battery module, resulting in prevention of performance degradation.
Cooling of cells for reducing temperature rise in the cells due to charge and discharge is essential for an electric storage device so as to improve battery performance, for example, to reduce variation in charge and discharge amount and lifetime of the cells.
In recent years, further improvement has been required for battery performance of an electric storage device. Means for achieving it include, as the related arts, further improvement in cooling performance of cells by providing the sub cooling passage in addition to the main cooling passage or by reducing the cross-sectional area of the passage in the battery case. However, although the related arts are effective for the electric storage device constituted with a battery module size of which is not restricted, they are not necessarily effective for the electric storage device made up with a battery module of a limited size, e.g. an electric storage device mounted in a small storage space as in an automobile. This encourages a new cooling structure that enables an improved cooling performance of cells.